Comment by Xirdus

11 days ago

The bug in the OP is about UNconditional impl. And honestly, looks like very standard code, definitely something that could've been written for real. I can't even explain why it passes checks, it clearly shouldn't.

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Xirdus

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dwattttt  11 days ago

This code, from the bug submission?

  impl<T: 'static + Send> Drop for Q<T> {
      fn drop(&mut self) { if let Some(t) = self.0.take() { KEPT.lock().unwrap().push(Box::new(t)); } }
  }

The bound on T in the Drop impl means Drop is not implemented for all T, only where T: 'static + Send. Q<T> also having the same bound doesn't make a difference to the Drop impl.

  • NobodyNada  11 days ago

    You cannot write a type which conditionally implements Drop: https://play.rust-lang.org/?version=stable&mode=debug&editio...

        struct Q<T>(Option<T>);

    impl<T: 'static> Drop for Q<T> {
        fn drop(&mut self) {}
    }


    error[E0367]: `Drop` impl requires `T: 'static` but the struct it is implemented for does not
     --> src/main.rs:3:9
      |
    3 | impl<T: 'static> Drop for Q<T> {
      |         ^^^^^^^
      |
    note: the implementor must specify the same requirement
     --> src/main.rs:1:1
      |
    1 | struct Q<T>(Option<T>);
      | ^^^^^^^^^^^

    • dwattttt  11 days ago

      Even if the bounds are the same on the struct and the impl, it's still true that placing bounds on the Drop impl means it's not implemented for all T (just all T that also satisfy Q).

      You also don't have to place those bounds on the Drop impl just because they're on Q, that's not an error.

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